Generation and transmission of high frequency oscillations



` Aung. Z6, 1941. A E, BQWEN 2,253,503

GENETION AND TRANSIISSIONv OF HIGH FREQUENCY OSCILLATIONS /Nl/E/vrof? ByA. E. BOWEN l AHORA/Ev Aug. 26, 1941.

A. E. BOWEN 2,253,503, GENERATION AND TRANSMISSION OF HIGH FREQUENCYOSCILLATIONS Filed Aug. e.. 193s 5 sheets-Sheet 2 F/c. 6 /36\ 38 3o 5 um l I BV I" Arm/m r Aus. 26, 1941. A. E. Bowl-:N 2,253,503l

,v GENERATION AND TRANSMISSION OF HIGH FREQUENCY OSCILLATIONS Filed Aug.6, 193B 5 Sheets-Sheet /A/VENTOR A. E. BOWEN Aug. ze, 1941.

I A. E. BOWEN l 2,253,503 `GENERATION AND TRANSMISSION OF HIGH FREQUENCYOSCILLATIONS FiledAug. 6, 193s 5 sheets-sheet 4 A. E. BOWEN ng. 26,l94v1.

GENERATION ND TRANSMISSION OF HIGH FREQUENCY OSCILLATIO-NS 5 sheets-smet5 FiledjAug. e, 1938 ATTO/QN Y Patented Aug. 26, 1941 CENERATION ANDTRANslvns sIoN oF nien FREQUENCY osoILLA'rIoNs Arnold E. Bowen, RedBank, N. J., assignor to Bell Telephone Laboratories, Incorporated, NewYork, N. Y., a corporation of New York Application August 6, 1938,Serial N 0. 223,426

15 Claims.

This invention relates to the art of transmission by ultra-highfrequency electromagnetic waves and more particularly to the generationand modulation of such waves. n

An object of the invention is to increase the efficiency with whichoscillations of ultra-high frequency are generated.

Another object is to increasethe harmonic power output and frequencystability of ahigh frequency oscillator. Y Y

The invention has for a more specific object an improvement in theefficiency, power output and other operating characteristics of anoscillation generator adapted for a system for the guided transmissionof electromagnetic waves through a metallic pipe.

In accordance with important embodiments of the present invention, theforegoing objectsjare realized in an oscillation system utilizing thetransmission cut-off characteristics of a metallic pipe guide, eitheralone or in conjunction with the phase velocity characteristics thereof,to se-` lect a desired harmonic or harmonics of an oscillation generatorto the exclusion of a fundamental and undesired harmonics, and moreparticularly in a preferred embodiment ofthe invention by inhibiting theabstraction of power from the oscillator at the fundamental andundesired harmonic frequencies. A principal feature of theseembodimeiits is that the fundamental frequency determining means servesalso to enhance the harmonic power output. In accordance with anotherembodiment of the invention, harmonic power is derived from amagnetronoscillator.

The nature of the present invention and its various objects, featuresand advantages will appear more fully in the following description ofseveral illustrative and specific embodiments, reference being made tothe accompanying drawings in which:

Figs. 1 and 2 are schematic drawings illustrating certain principlesutilized in accordance with the invention;

Fig. 3 shows a preferred form of oscillator in accordance with theinvention;` n

Fig. 4 is an equivalent circuit diagram applicable to Fig. 3;

Fig. 5 shows a detail of Fig. 3;

Fig. 6 illustrates a transmission system utilizing the presentinvention; Figs. 7 to 14E disclose wave type converters adapted for thesystem shown in Fig; 6;

Figs. 15, 16 and" 18 illustrate other forms of n. ui

oscillators in accordance with the invention, and Fig. 17 is an explodedview of a detail of Fig. 16;

Figs. 19 and 20 show combinations in which the oscillations generatedare applied to a twowire circuit; and

Figs.v 21 to 25 show alternative embodiments of the invention.

In some respects the present invention may be considered as animprovement on the invention disclosed and claimed in an application forLetters Patent, Serial No. 223,424, filed of even date herewith by G. C.Southworth.

' It has been shown heretofore that the interior of 'a metallic pipe canbe used for the transmission of certain types of high frequencyelectromagnetic waves, sometimes called dielectrically guided waves,provided the frequency of the waves exceeds a certain critical orcut-off frequency that is dependent on the type of wave, the transversedimensions of the pipe and the dielectric coefcient of the mediumfilling the interior of the pipe. These various types of dielectricallyguided waves are distinguished by their respective characteristicspacial distribution of the component electric and magnetic fields, andthey may beV represented as E01, En, H01, H11, etc. as indicated in thearticles by G. C. Southworth and J. R. Carson et al. appearing in theApril 1936 issue of the Bell System Technical Journal, Both of thesearticles disclose the critical relation that exists at cut-off betweenfrequency, dielectric coeliicient and diameter of guide for each of thefour principal types of waves mentioned above as transmitted through ahollow pipe of circular cross-section.

Referring now to Fig. 1, there is shown schematically a system thatillustrates certain principles involved in the present invention, andwhich comprises an oscillation generator S which is adapted to oscillateat a certain fundamental frequency f and at harmonic frequencies 2f, tf,Gf, etc., disposed within and near the closed end of a cylindricalmetallic pipe l containing a gaseous dielectric medium. The internaldiameter D of the pipe is fixed at such value that the criticalfrequency for dielectrically guided waves of the type launched from thesource S falls between some harmonic, say the nth harmonic fn, and thenext lower harmonic ffl-1. Under these circumstances and at somedistance away from the source S only the nth harmonic and higherharmonies appear, for all lower harmonics vand the fundamental aresuppressed by the high pass filter-like properties of the metallic pipeguide.

The electromagnetic eld associated with the oscillations of fundamentalfrequency and the harmonics below ,fn may be detected in the immediatevicinity of the oscillation generator, but because of the electricalproperties of the guide there is no corresponding flow of power throughthe interior of the pipe. If the metallic pipe is of copper or othergood conducting material there is also little loss of power in the wallof the pipe surrounding the oscillation generator. Accordingly, whilethere may be intense oscillations at the fundamental and lower harmonicfrequencies there will be little abstraction of power from theoscillation generator at these frequencies, and a much greaterproportion of the power supplied to the oscillator will appear in theform of harmonic frequency oscillations having frequencies fn andhigher.

If the source S is arranged to launch waves of the H11 type, forexample, then the expression for the critical relation existing atcut-off' is:

where D is the internal diameter of the pipe in centimeters, A the freespace wave-length corresponding to the cut-off frequency, and Kvthedielectric constant of the dielectric medium filling the pipe, K beingsubstantially unity where the medium is gaseous. The critical relationmay be expressed also in the form fedi/1.706 DJI? 2 where fc is thecut-olf frequency and c is the velocity of light in free space, 3 1010centimeters per second. Supposing for specific example that the diameterD is '7.5 centimeters, that the frequency of the fundamental oscillationis 1000 megacycles per second and that the dielectric medium is gaseous,the critical frequency is jc=3 10W/1.706 X 7.5 1:2344 megacycles/sec.

The critical frequency in this case, therefore, lies between the secondand third harmonics of the fundamental, these being 2000 and 3000megacycles/sec., respectively, so that the fundamental and secondharmonic are suppressed and only the third and higher harmonics aretransmitted.

To select from the nth and higher harmonics some particular desiredharmonic, there may be inserted in the guide a reactance spaced acritical distance from the source S, the latter also being spaced acritical distance from the closed end of the pipe. Fig. 2 shows asuitable arrangement in which the reactance takes the form of anapertured diaphragm 3, the diaphragm being spaced a distance Z2 from thesource, and the source a distance l1 from the end of the pipe. With theproper spacing of these elements and with the proper size of apertureonly the nth harmonic will be transmitted beyond the diaphragm 3.Moreover, this combination constitutes a transformer which transformsthe impedance of the guide to the value required for maximum transfer ofpower at the nth harmonic frequency from the source to the guide.Because the velocity of propagation varies with frequency, it isunlikely that an adjustment which is optimum for the selection of the11th harmonic will also permit one or more other harmonic frequencies tobe transmitted. If such other harmonics appear, or in any case, anotherapertured diaphragm 4 spaced a distance Z3 from diaphragm 3 may beprovided to form a band-pass filter so that all harmonics other than thenth are eliminated. Preferably the system is so proportioned that thedesired harmonic corresponds to fn, that is, so

that the harmonic to be isolated is the one lying next above the cut-01Tfrequency.

In accordance with a preferred embodiment of the invention especiallyadapted for the launching of guided waves of the H11 type, the source Stakes the form shown in Fig. 3. In this embodiment, oscillations offundamental frequency f are caused to flow within a shielded circuitcomprising a short-circuited coaxial conductor line which greatly aidsin preventing the loss of power by radiation at the fundamentalfrequency. Means are provided for obtaining optimum circuit impedancerelations for the fundamental oscillations, while favorable impedancerelations for the desired harmonic frequency are obtained by othermeans.

Referring to Fig. 3, a three-element discharge device 6, comprisinglamentary cathode, grid and anode, is disposed in a metallic turret 5over an opening in the wall of pipe I where it is out of the path ofwaves within the pipe. Diametrally across the pipe from the dischargedevice extends a coaxial conductor pair comprising an inner conductor I0and a tubular outer conductor II which respectively are connected at oneend to the grid and anode of the discharge device. Short-circuiting thecoaxial pair for high-frequency currents is a bridge I5 which isadjustable lengthwise within the coaxial pair to alter the effectivelength of line tied to the grid and anode. The bridge is shown in Fig. 5and it will later be described in detail.

Where the outer conductor II of the coaxial pair passes through the pipewall it is insulated therefrom but capaciti'vely connected thereto bymeans of a metallic plate I2, and it is held in position by a block I3of insulating material attached to the outer face of the pipe I. Overthe inner conductor I0 is coaxially disposed a hollow rod I4 the upperend of which is attached to the Vbridge I5 to control the positionthereof. For 'precise adjustment of the bridge, the rod I4 is externallythreaded land an adjusting nut I6 of insulating material is mounted onthe threaded portion, the nut being exposed for hand operation andrestrained from longitudinal movement by the block I3 on the one sideand a bridge I'I of insulating material attached thereto on the other.The lower end of rod I4 carries a vane I8 which rides in a longitudinalslot in a tubula`r -guide I9, thereby preventing rotation of the rod andserving as an indicator of the position of the short-'circuiting bridge.

The 'lament leads' 20 from the discharge device are brought out throughopenings in the pipe wall near the turret, and around each is a metallictube y2| which extends outwardly from the pipe and forms with theenclosed filament lead a coaxial conductor pair. An insulating bushingis provided* where each tube 2| is attached to the pipe. Each of thesecoaxial pairs is provided with a bridge 22 which is adapted to operateas a high-frequency capacitive short-circuiting means and which islongitudinally adjustable by means not illustrated.

Appropriate operating potentials may be applied to the elements of thedischarge device in any suitable manner. In the embodiment illustrated,filament heating current is supplied from a battery 24 connected betweenthe leads 20. A battery 25 connected between one of the filament leadsand the metallic plate I2 provides anode potential, and 1a grid circuitresistor R connected between the lowerextremity of the rod I Il and the'Iilamentvpermits self-biasing of the grid.

Unduly large values of resistance R `are to be avoided inasmuch as alow-frequency oscillation may otherwise be found to be superposed vonthe high-frequency oscillations at lower anode voltages.

Turning attention now to the high-frequency circuits, the oscillationsystem illustrated in Fig. 3 may be better understood by considering theanalogy it bears to the form of tuned-plate, tuned-grid oscillatorrepresented schematically in Fig. 4. In the latter there is a frequencydetermining circuit a connected between grid and anode. In Fig. 3 theportion of the coaxial line above the short-circuiting bridge I isanalogous, forv it also is connected between grid and anode and itslength substantially xes the fundamental frequency of oscillation. InFig. 4 there is a branch between the cathode and the mid-point of thetuned circuit a; acorresponding branch may be found in Fig. 3. Thus, thebridge I5 marks the mid-point of the circuit o, and a high-frequencypath may be traced from that point along the outer surface of conductorII to plate I2, thence around the inner surface of the pipe I, out alongthe inner surface of each of the conductors 2|, across bridges 22, andback along the filament leads 2i) to the cathode. Circuit b in Fig. 4repre sents the impedance in the branch just traced, and by means of thefilament circuit bridges 22 it may be adjusted over a wide range. Thesebridges may be so adjusted, in fact, that the impedance is substantiallyZero at the fundamental frequency of oscillation.

With the filament circuit coaxial units adjusted as last described,oscillations of great amplitude are set up, the amplitude being limitedby the emissivity of the filament and by the power lost from the systemin the form of heat. By keeping to a minimum the amount of insulatingmaterial in the high-frequency fields and by using conductors of lowresistivity the heat losses are kept to a small value, and the amplitudeof oscillations is limited primarily by the rate at which electrons canbe emitted from the filament. It is characteristic of oscillations thuslimited that there is a large proportion of harmonic power in the anodecircuit, which it will be understood is important with regard totheobjects of the present invention.

In the Lecher frame comprising the coaxial conductors I, II in Fig. 3,the velocity of wave propagation is substantially independent offrequency, thus differing from the phase Velocity characteristic of thedielectric guide. It follows that when the Lecher frame is tuned to afundamental frequency f, it is resonant also at the harmonicfrequencies, 2f, 3 f, etc., and serves the very important function ofreinforcing oscillations at these frequencies. Accordingly, the Lecherframe in Fig. 3 serves not only to fix the fundamental frequency ofoscillation but also to increase the power output at the desiredharmonic frequency or frequencies.

The harmonic currents in the system shown in Fig. 3 must flow along thediametral conductor I I where they can give rise to correspondingdielectrically guided waves of H11 type in the pipe I, or at least to`waves corresponding to such of the harmonics as lie above the cut-offfrequency of the guide. The harmonic current path may not be of optimumimpedance for the desired harmonic, but a favorable virtual impedancecan be realized by proper adjustment of the distance Z1 indicated inFig. 2f. Ready adjustability is possible if the cap closing the end ofthe pipe be replaced by a longitudinally adjustable metallic piston. i

Inone specic embodiment in accordance with Fig. 3 where the guide Icomprised a brass pipe having an internal diameter of 4% inches, freespace wave-lengths ranging continuously from 20.7 centimeters to 14.1centimeters were obtained with substantial amounts of power over theentire range. In this range the wave observed is the second harmonic ofa fundamental oscillation ranging in wave-length from 41.4 centimetersto 28.34r centimeters, and inasmuch as the latter wave-length range isabove the cut-off wave length for the particular pipe used, the eldassociated with the fundamental oscillation is conlined to the immediatevicinity of the oscillator. Under these circumstances, the amplitude ofthe second harmonic is much greater than it is when the oscillator isoperated in a pipe of diameter large enough to support the fundamental.

Preferably, as noted hereinbefore, the oscillation generator is disposedin a section of pipe the diameter of which is too small to support thefundamental oscillation or any harmonic oscillation up to the desiredharmonic.

Fig. 5 shows a preferred form of the short-circuiting piston I5 of Fig.3. The bridge comprises a cylindrical metallic collar 3| which slides oncentral conductor It) and which is internally threaded at its lower endto receive the threaded end of hollow rod I4. Surrounding member 3I is ametallic cup S2 which is of substantially the same external diameter asthe internal diameter of conductor II. vMica 35 or other suitableinsulating material separates members SI and 32 so that a conductiveshort circuit of the coaxial line is avoided. A metallic nut 33 on thethreaded portion of rodY I2 clamps the apertured bottom of cup 32 and isinsulated from the latter by mica or other suitable material 34. Theupper ends of members 3| and 32 are tapered and slotted so that goodcontact can be had between member 3| and central conductor lil andbetween member 32 and outer conductor II.

Fig. 6 illustrates a transmission system incorporating the oscillationgenerator of Fig. 3 as adapted for operation at a harmonic frequencyhigher than the second. Here the oscillator is interposed in a pipe Iwhich is terminated at the left in an adjustable piston 3o, the internaldiameter of the pipe i beimg, for example, 2% inches, so that the fourthharmonic of the fundamental oscillation is the lowest frequency that canbe transmitted. The length of pipe I is sufficient to insure completeattenuation of lower or der harmonics. The guide may then'be expanded toany convenient diameter and a pipe 36 employed for the distancetransmission of the waves. At the receiving end of the system arectifying device 3l disposed in the path of the waves and backed bypiston 38 may be used for efficient reception of the fourth harmonictransmitted. The harmonic wave may be modulated with telephone,telegraph or television signals occupying a Wide range of frequencies.

Whereas in Fig, 6 a shoulder is provided at the junction of guidesections I and 35, this is a convenient point to introduce means forchanging the type of wave from the I-Iii type launched from theoscillation system to a different type which, for one reason or anothermay be preferred for distance transmission through the main guide 36.Figs. 7 to 14E illustrate a `few `kinds of wave type convertersappropriate forthis purpose. Although these converters are disclosed asmeans forV changin'g from an H11 wave to .another type of wave, they arebilaterally operative and may be applied generally for operation in theopposite direction of transmission so as to convert the waves ofincident type to waves of H11 type.

The converter shown in longitudinal section in Fig. '7 and in successivecross-sections in Figs. 8A to 8F is adapted for operation in the systemillustrated in Fig, 6 to convert the incident H11 waves to E01 waves. Atapered pipe section is interposed between pipes l and 36, and a.diametral metallic sep-tum 39 is provided as shown, the septum beingaligned with the -electric eld of the applied H11 wave. Between points Aand D the septum expands I:from Ya point on the periphery of pipe l tothe vfull diameter of the pipe, then continues with the same width to dwhere the tapered pipe section begins. The septum is then graduallyan-'d symmetrically reduced in width and ends in an-axial rod 4i. Theprinciple of operation of the converter may be understood by referringto the cross-sectional views comprising Figs. 8A to 8F, and bearing inmind that lines of electric force, represented by 'the dotted lines,tend to meet any conducting surface perpendicularly. In effect, theincident H11 wave is progressively distorted by the septum so that atpoint D 'two oppositely phased H11 waves are 'made to -appear. Betweenpoints d and F these in turn are modified bythe septum and merged intoan E01 wave. Preferably, the lengths of the two tapering portions of theseptum are large compared with the operating wave-length. Optionally, anappropriate grating 42 may be provided around rod 4| to insure that onlywaves of E01 type are delivered to guide 36. The diameter of guide 3Smust of course be greater than the critical diameter for E01 waves.

Figs. 9 and 10A to 10D show another form of HHEM converter that has theadvantage over the converter last described in that a lesser degree ofprecision in locating the septum is permissible. In this case thediametral septum 43 is tapered from a point on the periphery of the pipeat A to a width equal to the radius of the pipe at B, and it ismaintained at this width to .point b from which it is tapered down to anaxial rod 4|. Figs. 10A to 10D show how the wave is progressively modiedby the septum.

Figs. 11 and 12A to 12F show a converter for changing an H11 Wave to anH01 wave. Here the incident H11 wave is rst modified by the bifurcatedportion of septum 44 to establish at point D two oppositely phased H01waves in respective semi-cylindrical guide portions. The internal radius.of one of these guide portions is then reduced as indicated in Fig 12Eso las to change the velocity of propagation of the Wave within thatportion. The portion of reduced radius extends to the end of the septumand it is made of such length that a relative phase reversal of thewaves in the two semi-cylindrical portions is obtained, whereby the twocoalesce to form a single H01 wave in the guide 3B.

'Ihe converter shown in Figs. 13 and y14A to 14E is adapted forinterconversion of H11 waves and E11 waves. In this embodiment a pair ofdiametrally aligned septa 45 are provided which are progressivelyincreased and decreased in width in the manner illustrated vandterminated in a 4pair of longitudinal rods T45. The cross- Sectionalviews comprising Figs. 14A to 14E show the progressive changes in theelectric field of the waves.

Other examples of practice in accordance with the invention are shown inFigs. 15 to 18, where the discharge device is one in which lgrid and.anode terminals `are brought out on both sides of the enclosing glassenvelope.

In the embodiment illustrated in Fig. 15 the discharge device isdisposed near the axis of the pipe, and to one set of grid and anodeterminals there is connected a pair of conductors 26 which extend awayfrom the device parallel to the axis of the pipe. The conductor pair iscapacitively short-circuited near its distant end by an adjustablebridge 40, which is shown schematically. To the other set of electrodeterminals is connected a similar conductor pair 26' which extends in theopposite direction and which also is provided with an adjustable bridge40. At right angles to the plane of the Lecher system thus formed lieanode and grid leads 21 and 28, respectively, which are terminated, forhigh-frequency currents, at the pipe wall by respective condenserplates. Filament leads 29 extend in the opposite direction to individualcondenser plates. Operating potentials can be supplied to the electrodesby connections extending through openings in the pipe wall to theseveral plates.

In Fig. 16, a conductor pair 2G and adjustable bridge 43 are provided.as in Fig. 15, and also a 4corresponding conductor pair 25. In lieu ofbridge 40', however, provision is made in the end assemblage of theguide as shown in exploded form in Fig. 17. This assemblage comprises ametallic end cap 50 and three 'thin metallic discs stacked against theinner face of cap 50 with discs of mica or other suitable insulatingmaterials separating them. To the innermost metallic disc 49 is attachedthe member of conductor pair 26 that is connected to the grid. To thenext disc 48, and passing through an opening in the first one, isconnected the other or anode member pair 26. The third disc is dividedvertically into two semicircular portions 41a and 41h, and from eachportion there extends thro-ugh the end cap 50 a tubular conductor which,together with a respective longitudinal lead f from the lament comprisesa coaxial conductor line 2|. A Capacitive -short-circuiting bridge 22 ineach coaxial line permits of lament circuit tuning as in Fig. 3. Leads pand g are brought out longitudinally from discs 48 and 49, respectively,through openings in the intervening discs and endcap, for connection tothe external circuit elements.

The preferred varrangement where H11 Waves are to be generated in thepipe guide and the discharge device is of the double-ended typedescribed with reference to Figs. 15 and 16, is i1- lustrated in Fig.18. It embodies several of the constructional features and advantages ofthe arrangement shown in Fig. 3, but as contrasted With the latter thedischarge device B0 is farther from the -guide I the `'metallic chamber52 enclosingthe 'device being connected with the interior of -the'pipe Ithrough a tubular metallic neck 5I. Through the latter and diametrallyacross the wave guide extends the coaxial conductor tuning and wavelaunching structure IO-l I, which at its upper end is connected to the:grid and anode of the discharge device and at its lower end isassociated with the mechanism for adjusting the position of thecapacitive shortcircuiting piston I5, all as in Fig. 3. The tunablecoaxial filament leads 2| are conveniently brought out radially from thebase of the chamber '52, as shown, and need not be insulated therefromif the respective pistons are of` the capacitive type such as shown inFig. 5. The external circuits may be the same as those in Fig. 3 andsimilarly connected to the discharge device. The upper end of conductorI affords an alternative grid connection.

The Locher frame in Fig. 18 is completed by another coaxial conductorline I0'-I I connected tothe other pair of grid and anode terminals ofthe discharge device 60 and adjustably shortcircuited by the condenserpiston I5. The means provided for adjusting the position of piston i5 issubstantially the same as that provided for piston i5 in the otherportion of the Lecher system and the primed reference characters Willserve to identify corresponding elements. Another tunable coaxialconductor system is formed by conductor il and metallic pipe 53 whichextends upward from chamber 52 to bridge I3' and encicses the upperportion of the Lecher frame. This coaxial system is short-circuited by acondenser piston 55 which may be of the type shown in Fig. 5. piston 55are not illustrated, but any suitable mechanical arrangement can beemployed for the purpose. For example, the piston may be provided withears or lugs which ride in longitudinal slots in pipe 53 and externalplates arranged to cover the exposed portions of the slots.

The adjustment and operation of the combination shown in Fig. 18 is asfollows. 'vI'he wavelength of the fundamental oscillation is xedprimarily by the distance between short-circuiting pistons i5 and I'5;experiment has shown that this distance is materially less than one-halfof the fundamental wave-length. The construction of the device of Fig.18 is such that with a given interval between pistons I5 and I5 theelements of discharge device 6) can be effectively moved ashcrt distanceto one side or the other from the mid-point'of this interval. Experiencehas shown that ordinarily the best output is secured when the elementsare near the middle ofV the interval, although the exact adjustmentsrequired vary from tube to tube. These adjustments havingbeen made,adjustment of the lament tuning pistons further enhances theoscillation.

Now it has been pointed out in connection with Fig. 3 that since nofundamental frequency powerA isderived from the oscillation circuitexcept that resulting from ohmic and dielectric loss, the fundamentaloscillation builds up to high amplitudes, and the oscillating currentcontains a substantial amount of-harmonics. Harmonic power can beabstracted, because guide I is of such diameter as to support a Wave ofharmonic frequency. An instructive way to look at what transpires is toconsider that the part of coaxial Ii contained within guide I representsan impedance connected to the source 60, an impedance possessing aresistive component by virtue oik the energy flowing from it down guideIand a reactance by virtue of the presence of the reflecting piston 313,(shown in Fig. 6), in guide I. Eachof these components may be varied,a1- though not independently, by varying the position of the reiectingpiston 30. Also shunted on the source Si! is the outer coaxial II-'53with adjustable piston 55. This supplies an independently adjustablereactance element in Means for adjusting the position of i shunt withsource 6E). Then the source having been adjusted for maximum intensityof oscillation at the fundamental frequency as described heretofore,maximum output at a desired harmonic requires first, adjustment of thepiston 35 in guide I to secure a match between the resistance componentof the impedance of coaxial II and the internal resistance of source 55,and second, adjustment of piston 55 to secure optimum reactanceconditions, that is to say, approximate neutralization of the reactanceof coaxial Il.

Figs. 19 and 20 illustrate how the guided waves of harmonic frequencyproduced by a combination such as shown in Fig. 3, for example, can beconverted into ordinary conduction rcurrents in a two-wire circuit andthus made available for general application. In Fig. 19 the cylindricalmetallic shield 55 surrounding a two-wire line 58 extends axially intothe oscillator pipe I and it is terminated with a piston-like annularflange 5l which is adapted to slide within the pipe. The conductors 58extend beyond the flange 5l an adjustable distance d2 and thenceradially to opposite points on the pipe wall so that the radial portions59 are in alignment with the electric iield produced by the oscillator.The distance d1 between the oscillator and the conductor portions 59 ismade large enough to'insure suppression of fundamentaland unwanted lowerharmonic frequencies by the filter-like properties of the pipe guide I,and additional filtering means may be inserted in this portion, ifdesired. The distances di and d2 are then so adjusted as to produce amaximum transfer `of energy into the shielded pair at the desiredharmonic frequency or frequencies.

The combination shownA in Fig. 20 is substantially the same inconstruction and operation as the one last described, except that thetwo-wire line comprises a coaxial conductor pair 55-6L the innerconductor 6I Aof which is terminated in a single radial conductor 52aligned with the incident electric field.

For the production of harmonic waves of symmetric electric or Eloi type,the arrangement shown in Fig. 2l may be used. It is similar to thecombination illustrated in Fig. `18 in that the same kind of dischargedevice, frequency determining means, tuning adjustments and housing maybe employed and it is illustrated in Fig. 21 as comprising all of theFig. 18 structure that lies above the junction of neck 5i and guide I.'I'his structure is mounted at the end of a metallic pipe guide I withthe inner coaxial system Iii-H projecting axially into the pipe throughtheend cap thereof, the latter being arranged as arange at the end ofnecl: 5i. Electrical connection to the anode may bemade at the end oftubular conductor II', and to the grid at the end of inner conductorIil. The manner of adjustment is the same yas that described withreference to Fig. 18, and the manner of operation is essentially thesame except that the conductor i I cooperates with the adjacent portionsof pipe I and neck 5I to launch waves of symmetric electric type.Restriction of the diameter of pipe I permits suppression of theoscillations of fundamental frequency, and reactors 3 and i may beutilized to discriminate between the various har- Vrnonics that appearas described hereinbefore.

In the examples hereinbefore presented the source of harmonic power hasbeen a primary source, that is, one 'in which a continuous power input,derived from batteries, for example, is converted by some mechanism intoan alternating current output having a certain fundamental frequency.Figs.A 22 and 23 illustrate embodiments in which the primary source isused to drive a secondary source, viz., a harmonic generator.

In Fig. 22 the primary source is a diode oscillator S comprising anevacuated chamber formed within cylindrical metallic pipe B3 between themetallic end cap 64 thereof and glass seal E5. The lamentary cathode 6Bof the diode is disposed in close proximity to the center of end cap 64,the latter constituting the anode. The frequency of oscillation isdetermined by the size of the. cavity that is bounded at one end by cap64 and at the other by aperturedmetallic diaphragm 61. The leads tofilament 66 are brought substantially axially through pipe 63 and theaperture in diaphragm B1 into capacitive relation with a metallic plate68, thence radially in opposite directions through the walls of the pipewhere they are continued as. the central conductors of capacitivelyshort-circuited coaxial units 69, the outer conductors of which areinsulated from pipe 63.

At its upper end, pipe 63 terminates. at an opening in the wall ofmetallic pipe guide l, and within the opening is disposed athree-electrode discharge device 1G, the grid. electrode of whichextends inall directions beyond its enclosing glass envelope to coverthe end of pipe 63. The anode of device 10 lies within guide l and theconnection thereto extends diametrally across the guide and through anopening in the opposite side to a suitable source of direct currentpotential. This diametral lead serves to launch in the wave guide IWaves of the H11 type. The filamentaryy cathode of the device 1U liesonthe other side ofV the grid and the connections 'thereto are broughtaxiallyv through pipe 53 into capacitance relation with plate 63,thenceradially through laterally extendingcoaxial units 1I. Pipe 63 isconductively broken at the overlapping joint 12. Coaxial units 69 and 1|may be tuned to exclude high-frequency currents from the externalfilament circuits.

In theoperation ofv the combination shown in Fig; 22 oscillations offundamental frequency from the diode are transmitted as coaxialconductor waves to the cathode-grid region of discharge device Thelatter is operated with the grid biased negatively with respect to thecathode so that ordinarily little or no space current flows from thecathodeto the anode. Under these circumstances the output of device 10is rich in har- :monies of 'the fundamental frequency applied and anydesired harmonic may be selected by proper restriction of the diameterof pipe I and by proper adjustment of the iris diaphragms in accordancewith principles hereinbefore described.`

In Fig. 23 the primary source S. is disposed.. near the closed end of ashort section of metallic.

put is rich in harmonics and the diameter of4 wave guide and theadjustment of the iris diaphragms is such as to select the desiredharmonic. Whereas 'the source S` is shown as a primary source-it maycomprise a device such as discharge device 1U disposed in a commonboundary between guide section 15 and another guide section not shownand driven by a primary or harmonic source in the added section ofguide. In fact, the.v harmonic generating stages can be concatenated inany desired degree to the end that the primary source has a frequencylow enough that it may be controlled by a piezoelectric crystal or otherfrequency controlling means. Thus the desirable feature of greatconstancy in the frequency` of the ultimately derived harmonic wave canbe secured.

I have found that in a split-plate magnetron oscillator operated in thedynatronic mode of oscillation there is a strong double frequencycurrent in the common lead to the split plates. One object of myinvention is to provide means for accentuating this double frequencycurrent and delivering its power to a load to the substantial exclusionofthe oscillations of fundamental frequency. Another object is toincrease the double frequency or second harmonic power output of anoscillator. ofA the kind described, relative to the power output at thefundamental frequency of oscillation. In accordance with theillustrative embodiment of this phase of my invention as shownschematically in Fig. 24, where the load comprises a metallic pipeguide, the foregoing objects are realized in a, combination utilizingthe high-pass filter characteristic of the metallic pipe guide.

The usual split-plate magnetron comprises a pair of anodes that arespaced apart on opposite sides of a iilamentary cathode and so shaped asto form a substantially cylindrical open-ended chamber coaxial with thefilament. Means are provided for establishing a strong unidirectionalmagnetic nei-d within and parallel to the axis of 'the chamber, and aLecher frame or other tuned. circuit is connected to the anodes for xingthe frequency of oscillation. In some cases the plate is split into morethan two parts, but the type having two anode elements will suffice forillustration of the invention. A direct current source, which mayconveniently be connected tothe electrical mid-point of the tunedcircuit, biases the two anodes equally and positively with respect tothe cathode. Strong oscillations even at frequencies above a billioncycles per second have been obtained. The practical construction,adjustment and operation of oscillators of this kind are details wellknown to those skilled in the art and need no elaboration here.Reference is made in this connection to the paper by G. R. Kilgoreappearing in the August 1936 issue of the Proceedings of the Instituteof Radio Engineers. pages 1140-1157, and particularly to Fig. 13thereof,

Referring now to Fig. 24 a magnetron is shown schematically ascomprising two semicylindrical anodes 8.5 surrounding a filamentarycathode 86, and av fundamental frequency determining Lecher wire system81, the open end of which is connected to the anodes, all enclosedwithin an evacuated glass vessel. This combination is disposed within ametallic pipe 9U with the wires of the Lecher system parallel to theaxis thereof. The filament leads B8 are brought out togethersubstantially axially through pipe and through a central aperture in themetallic cap 99 which closes the end ofthe pipe, and the common lead 9|to the split plate extends axially in the other direction from theshort-circuited end of the Lecher system and is connected eventually tothe anode voltage source.

To obtain the required magnetic field an electromagnet may be employedas shown in Fig. 25 in which the pole-pieces 96 extend through oppositeopenings in the wall of pipe 99 into close proximity to the ends of thelamentary cathode 86. These pole-pieces are shown as carrying directcurrent windings 91, and the magnetic circuit is closed through therectangular yoke 95. Optionally, theA glass envelope may be replaced byglass seals disposed across pipe 99 on opposite sides of the magnetron.

It can be shown theoretically Aand I have demonstrated experimentallythat a strong second harmonic electromotive force is developed betweenthe cathode and the terminal connected to the anode voltage source, thatis, the terminal atthe short-circuited end of the Lecher frame, and thatthere is substantially no fundamental frequency component between thesetwo points. Ordinarily thisY double frequency electromotive force isshort-circuited by the external cathodeanode circuit and no use is madeof it, power being abstracted from the oscillator substantially only atthe fundamental frequency as by connecting the load across the twoanodes. The arrangement shown in Fig. 24, however, enables efficientabstraction of power at the harmonic frequency and at the same timesuppresses dissipation of power at the fundamental frequency. In thelatter respect, it is similar to other embodiments of the inventionhereinbefore described. As in these other embodiments the oscillator iscompletely shielded and so larranged that powerv can escape from itsimmediate Vicinity substantially only in the form of dielectricallyguided waves of frequencies greater than the fundamental frequency ofthe oscillator.

Thus in Fig. 24 the wave guide load comprises' the metallic pipe I, andthe oscillator pipe 99 branches from it radially in one direction Withthe anode lead 9| extending diametrally through the pipe I so thathigh-frequency currents in the anode lead can give rise todielectrically guided waves of asymmetric magnetic or H11 type withinthe pipe I. Branching radially in the opposite direction is a pipe 92,conductively insulated from guide I, and through it conductor 9I iscarried axially lto form a coaxial conductor line capacitivelyshort-circuited by an adjustable piston 93. Guide I is terminated in amovable reflecting piston 3l] which is to be adjusted in positionconcurrently with adjustment of piston 93 until a combination is foundfor which the second harmonic power output to the guide I is a maximum.An increase in the power output may sometimes be had by shifting themagnetron longitudinally within the pipe 99. To insure against escape ofpower from the oscillation system at the fundamental frequency, thetransverse dimensions of the guide I are so restricted that thetransmission cut-off frequency lies between the fundamental frequencyand the second harmonic frequency.

Where signals are to be impressed on the selected harmonic, it has beenfound that any modulation system in which the amplitude of thefundamental oscillation is modulated introduces a component of frequencymodulation as well. This result is objectionable inasmuch as it ispreferred that the wave be either solely amplitude modulated or solelyfrequency modulated. The devices described in this application areadapted to produce amplitude modulated Waves if the modulation isperformed on the harmonic rather than on the fundamental wave. This canbe done as illustrated in Fig. 24 by interposing in the path of theselected harmonic wave in the guide I an attenuator, the resistance ofwhich depends upon the voltage applied to it by the signal source G. Theparticular attenuating device shown comprises a neon'or other gasdischarge tube M so proportioned that the discharge forms a barrier orscreen across the guide I. The intensity of the discharge andconsequently the modulation of the guided wave, is controlled by themodulating source G. The modulator M might be replaced by a rod or discof some material having a non-linear resistancevoltage characteristicarranged so that the modulating source controls the resistance of thedevice.

Although the present invention has been described with reference tovarious specific embodiments it will be understood that these areprimarily illustrative and that the invention includes such otherembodiments as come within the spirit and scope of the appended claims.

What is claimed is:

1. In combination, a wave guide comprising a metallic pipe, anoscillation generator for launching in said guide ultra-high frequencywaves of a character such that the guide presents to them thecharacteristic of a high-pass filter, said generator comprising afrequency controlling Lecher system tuned to the fundamental frequencyof operation and to harmonics thereof, and a reflector in said guidespaced in one direction from said generator a distance that is optimumwith respect to the launching` of waves of harmonic frequency in theopposite direction, said distance being non-optimum for the launching ofwaves of said fundamental frequency.

2. In combination, a metallic pipe for the transmission ofdielectrically guided waves, a metallically shielded enclosure openinginto said pipe, an oscillation generator comprising a space dischargedevice in said enclosure, a shielded transmission line constituting aLecher system for controlling the fundamental frequency of oscillationand enhancing harmonic oscillations, and means excited by said harmonicoscillations for establishing corresponding guided waves in said pipe.

3. A combination in accordance with claim 2 comprising circuit means forcontrolling the impedance of said generator to oscillations of saidfundamental frequency.

4. A combination in accordance with claim 2 comprisingmeans forcontrolling the impedance presented to said pipe at differentfrequencies.

5. A combination in accordance with claim 2 comprising a reector in saidpipe spaced in one direction from said generator a distance that isoptimum for the launching of waves of harmonic frequency in said pipe.

6. In combination, a wave guide comprising a metallic pipe, ametallically shielded enclosure branching from said pipe, a spacedischarge device in said enclosure, said device having at least threeelectrodes, means adapting said device to generate ultra-high frequencyoscillations comprising a short-circuited, shielded transmission lineconnected to two of said electrodes, and a conductor extending from theshort circuit transversely of said pipe, along a path conforming withthe-transverse electiic eld of a wave adapted for. dielectrically guidedpropagation through said pipe, into electrical connection with the thirdof said electrodes, the cut-off frequency of said guide being higherthan the lowest frequency at which said line is resonant, and areflector across said guide. spaced a distance one Way from saidconductor that is substantially optimum for the reenforcement of aguided wave harmonically related to said lowest frequency.

7. A combination in accordance with claim 6 comprising tuning means inthe connection between said short circuit and said third electrode forminimizing the circuit impedance at said lowest frequency.

8. In combination, a guide for high-frequency electromagnetic wavescomprising a metallic pipe, an oscillator comprising a space dischargedevice and a Lecher system for Xing the fundamental frequency thereof,means energized by harmonic oscillations from said oscillator forlaunching corresponding dielectrically guided Waves in said pipe, areflector within said pipe spaced in one direction from said launchingmeans for enhancing the transmission of waves in the other direction,and an adjustable reactor for controlling the impedance presented bysaid oscillator to said launching means.

9. In combination, a metallic pipe guide, a reflector across said guide,a Lecher frame disposed longitudinally within said guide andsubstantially coaxial therewith, said Lecher frame being short-circuitedat one end by means cornprising said reflector, and an oscillatorcomprising a space .discharge device interposed in said Lecherframe, thecut-oi frequency of said guide being higher than the fundamentalfrequency to which said Lecher frame is tuned.

l0; A dynatronic oscillator comprising a splitplate magnetron having acathode and a pair of anode segments, circuit means tuned to thefundamental frequencyv of said oscillator and 'connected across saidpair'ofY anode Segments, a circuit conjugate to said tuned circuit meansand connecting said pair of anode segments through a common lead to saidcathode, a useful load, and

means coupling said load to said common lead inoscillatory powertransfer relationv with harmonic 4currents in said common lead.

11. A combination in accordance with claim 10 in which said couplingmeans has frequency selective characteristics whereby it discriminatesagainst currents of fundamental frequency.

12. A combination in accordance with claim l0 in which said connectingcircuit is connected between said cathode and a nodal point of saidtuned circuit means.

13. A combination in accordance with claim 10 in which said connectingcircuit is connected between said cathode and a nodalV point of saidtuned circuit means, and in whichV said load` and coupling means havefrequency selective characteristics whereby they are receptive tocurrents of second. harmonic frequency.

14. In combination, an oscillator comprising a split-plate magnetronadapted for oscillation in the dynatronic mode, a metallic pipe, acircuit comprisingV a common lead to. the splitv plates, at least aportionof said lead comprising means within saidpipe for launching wavesof harmonic frequency therein, the transverse dimensions of saidpipebeing sorelated to theY fundamental frequency of said oscillator thatthe cut-off frequency of said pipe is greater than said fundamentalfrequency.

15. In combination, a split-plate magnetron adapted for oscillation inthe dynatronic mode, frequency determining means comprising a tunedtransmission line connected to the split plate, a wave guide comprisinga, metallic pipe, a chamber v comprising a metallic pipe branching fromsaid guide and enclosing said magnetron and said means, another pipebranching oppositely from said guide, acommon plate lead connected tothe electrical mid-point of said transmission line for the conduction of`second harmonic currents, said lead extending through said chamber andsaid other pipe, means for tuning said lead, a reector in said guide,said tuning means `and said reector beingrso adjusted as to enhancewaves of second harmonic frequency launched into said guide.

ARNOLD E. BOWEN.

